1. Field of Invention
The present invention relates generally to the field of wireless communication and data networks. More particularly, in one exemplary aspect, the present invention is directed to enhanced methods and apparatus for coordinating cellular base stations using backward error correction.
2. Description of Related Technology
Universal Mobile Telecommunications System (UMTS) is an exemplary implementation of a “third-generation” or “3G” cellular telephone technology. The UMTS standard is specified by a collaborative body referred to as the 3rd Generation Partnership Project (3GPP). The 3GPP has adopted UMTS as a 3G cellular radio system targeted for inter alia European markets, in response to requirements set forth by the International Telecommunications Union (ITU). The ITU standardizes and regulates international radio and telecommunications. Enhancements to UMTS will support future evolution to fourth generation (4G) technology.
A current topic of interest is the further development of UMTS towards a mobile radio communication system optimized for packet data transmission through improved system capacity and spectral efficiency. In the context of 3GPP, the activities in this regard are summarized under the general term “LTE” (for Long Term Evolution). The aim is, among others, to increase the maximum net transmission rate significantly in the future, namely to speeds on the order of 300 Mbps in the downlink transmission direction and 75 Mbps in the uplink transmission direction.
In parallel, further advancements of 3GPP are being investigated within LTE towards an IMT-Advanced radio interface technology, referred to as “LTE-Advanced” or “LTE-A”. Details regarding scope and objectives of the LTE-Advanced study are described at, inter alia; RP-080137 entitled “Further advancements for E-UTRA (LTE-Advanced)” to NTT DoCoMo et al., the contents of which are incorporated herein by reference in its entirety. The IMT-Advanced activities have been commenced and are guided by ITU-R (International Telecommunications Union-Radio Communication Sector). Key features to be supported by candidate IMT-Advanced systems have been set by ITU-R and include amongst others: (1) high quality mobile services; (2) worldwide roaming capability; and (3) peak data rates of one hundred (100) Mbps for high mobility environments, and of one (1) Gbps for low mobility environments.
The current discussions in 3GPP related to LTE-A are focused on the technologies to further evolve LTE in terms of spectral efficiency, cell edge throughput, coverage and latency based on the requirements in 3GPP TS 36.913: “Requirements for further advancements for E-UTRA (LTE-Advanced)”, which is incorporated herein by reference in its entirety. Candidate technologies include (1) multi-hop Relay; (2) downlink network Multiple Input Multiple Output (MIMO) antenna technologies; (3) support for bandwidths greater than twenty MHz by spectrum aggregation; (4) flexible spectrum usage/spectrum sharing; and (5) Coordinated Multipoint Transmission/Reception (CoMP). These proposed technologies are based on the requirements of 3GPP TS 36.814: “Further advancements for E-UTRA—Physical Layer Aspects”, which is incorporated herein by reference in its entirety. Backward compatibility with legacy LTE networks is also an important requirement for future LTE-A networks, i.e. an LTE-A network also supports LTE user equipment (UE), and an LTE-A UE can operate in an LTE network.
Coordinated Multipoint Transmission/Reception (CoMP) Operation
The aforementioned Coordinated Multipoint Transmission/Reception (CoMP) is one proposed approach for improving high data rate coverage, cell-edge throughput and or system throughput. FIG. 1 illustrates one exemplary CoMP deployment scenario 100 of an LTE-Advanced network comprising seven (7) cells, each cell is served by an associated base station 104. As shown in FIG. 1, a UE 102 receives data coverage from three (3) cells (Cell 1 104A, Cell 2 104B, and Cell 3 104C) which have been “coordinated” to minimize interference with one another. During operation, each one of the coordinated base stations manages control and user data transmissions with the UE according to a specific coordinated schedule. Thus, the UE receives control and user data from only one of the transmitting cells at any time.
During CoMP operation, the UE 102 maintains a distinct dialog with each of its coordinated base stations (i.e., both serving 104A, and supplemental base stations 104B, 104C) for control and data signaling. For example, error correction (such as Hybrid Automatic Repeat Request (HARQ)) is independently managed between each BS and the UE. The independent nature of prior art signaling increases appreciably in proportion to the number of concurrent connections. Thus, in the exemplary scenario of FIG. 1, the UE and Radio Access Network must maintain three (3) independent HARQ software processes, and their associated network resources (e.g., subframes, bandwidth, etc.).
Consequently, improved methods and apparatus are needed to optimize the overhead associated with multipoint topologies in wireless (e.g., cellular) networks. Ideally, such improved methods and apparatus should minimize the interference between each of the BSs, and improve overall error correction capabilities of the coordinated cells. Moreover, wireless networks that implement these methods and apparatus may substantially improve resource utilization, inter alia, by reducing transmit power, and error correction latency.